1. Field of the Invention
This invention relates to a method for forming a thin film of ultra-fine particles, and an apparatus for the same, and more particularly to a method for forming a thin film of ultra-fine particles and an apparatus for the same by which a thin film of ultra-fine particles is formed on an inner wall surface of a hole smaller than 12 .mu.m in diameter, and having an aspect ratio of larger than one.
2. Description of the Prior Art
Among methods for forming a thin film, there are a sputtering method, a deposition method, a physical vapor deposition method (PVD) such as an ion-beam deposition method, a chemical deposition method (CVD), a plating method and any other liquid phase film-forming method. In the physical vapor deposition method, atoms or molecules as film-forming material move in a straight line, from the generating source. Accordingly, positions on the base body on which a thin film should be formed, depend on the geometrical arrangement or mechanical arrangement of the generating source of the film forming material and of the base body. It is almost impossible to form a uniform film on an inner wall surface of a fine hole of large aspect ratio or a groove of the similar size, in the base body, since the straight flight line of the film forming material does not reach there. On the other hand, it is possible to form a relatively uniform film on the above fine hole or groove, by the CVD method or liquid phase film forming method. However, it is unavoidable that any impurities are mixed into the formed thin film.
Among methods for forming thin films of ultra-fine particles, there are a so-called "Gas Deposition method" or "Jet Printing method" in which a transport pipe and jet gas for transport are used to form locally a thin film, and "Cluster ion beam method" in which ionized grain beams are used. However, also in these methods, the film forming condition is limited by the geometrical or mechanical arrangement of the generating source of the film forming material and of the base body. Further, there is the method in which ultra-fine particles are sinked or precipitated from the liquid phase. However, in this method, a surface tension acts between the. inner wall surface of the hole or grove, and so it is difficult to form uniformly a thin film. Accordingly, this method cannot be widely used.
As above described, it is difficult to form a uniform thin film without impurity, on the inner wall surface of the fine hole or groove, by the above Prior Art thin film forming methods. Accordingly, in one case a high-integrated semiconductor device, in which via holes are made having an aspect ratio of larger than one, and a line width equal to a fraction of a .mu.m or smaller is subject to various limitations of manufacture. In another case it is difficult to form a uniform film of activated metal on the inner wall surface of fine holes on a catalyst carrier of high performance.
As an example, a base body S in which fine holes or grooves are made, is schematically shown in FIG. 1. A film 2 of silicon oxidate as insulator is formed on a silicon substrate 1. Another film 3 of aluminium is formed on the film 2. A fine groove 4 is formed in the film 2, and it is filled with aluminium. A second silicon oxidate film 5 is formed on the aluminium film 3. A second groove 6 is made in the film 5, and its bottom is the upper surface of the film 3. A via hole 7 with the bottom which is the upper surface of the film 3, is made in the groove 6. The groove 6 is 0.1 .mu.m in width, and 0.3 .mu.m in depth. The via hole 7 is 0.2 .mu.m in diameter, and 1 .mu.m in depth. The aspect ratio of the groove 6 is equal to 3, and that of the via hole 7 is equal to 5. It is difficult to form a thin film of metal, or particularly, high-melting metal or ceramics, onto the inner wall surfaces of the groove 6 and via hole 7, by the Prior Art PVD method